Power saving is becoming an important issue for network devices, due in part to the rapidly growing Internet and increasing bandwidth requirement from end users, as well as a generally increasing energy cost.
Link aggregation according to IEEE 802.3ad, is widely used to increase bandwidth between two network entities. For example, link aggregation is used at the aggregation level of Mobile Backhaul, Metro networks, and Optical networks. IEEE 802.1ax (former clause 43 of IEEE 802.3) standard has defined the mechanism for a Link Aggregation Control Protocol (LACP). LACP enables one or more links to be aggregated together to form a Link Aggregation Group (LAG). This allows a Media Access Control (MAC) Client to treat the LAG as if it were a single link.
Link aggregation achieves higher bandwidth by combining several full duplex point-to-point links, e.g. operating at the same data rate. It also increases availability since a single link failure will not cause the LAG failure as a MAC Client.
LACP works by sending frames or LACP Data Units (LACPDUs) down all links that have the protocol enabled. If there is a device on the other end of the link that also has LACP enabled, LACP will also independently send frames along the same links enabling the two units to detect multiple links between themselves and then combine them into a single logical link. LACP can be configured in one of two modes: active or passive. In active mode it will always send frames along the configured links. In passive mode however, it acts as “speak when spoken to”, and therefore can be used as a way of controlling accidental loops (as long as the other device is in active mode).
Links may be dynamically added or removed from a LAG. Upon a detected link failure, the LAG dynamically routes traffic on active links, guaranteeing traffic delivery although at a reduced rate. Thus, the LAG provides redundancy. LACP uses a Hash function to uniformly balance the traffic load among all the active links. The LACP mechanism can dynamically adjust the number of aggregated links according to a negotiation between peer ends.
In “Power saving mechanism based on Simple Moving Average for 802.3ad Link Aggregation”, Hideaki Imaizumi, GLOBECOM Workshops, 2009 IEEE, Nov. 30, 2009-Dec. 4, 2009, a power saving mechanism for LAG is based on Simple Moving Average. The method relies on a negotiation protocol (handshake) for both nodes connected to an aggregated link, to send messages between the nodes. An estimation algorithm is used to estimate an appropriate number of active links to comprise the aggregated link in accordance with the current rate of traffic outbound on the link. The estimation algorithm and the adoption of a dedicated handshake messages introduce a relatively long reaction time before the number of active links is varied. In addition, this arrangement may result in interoperability issues if the nodes have different manufacturers, due to possible handshake sequence misalignments or proprietary behaviors. Furthermore, such a system may not allow backward interoperability with legacy nodes operating a LAG.
Related issues apply to Multi-Chassis Link Aggregation Group (MC-LAG) or Distributed Resilient Network Interconnect (DRNI).